The present invention relates to an apparatus for detecting change in the height of each of axle portions respectively corresponding to pairs of front and rear wheels of a vehicle and for controlling an irradiation direction of a lamp thereof according to change in the attitude thereof.
There is known an apparatus (what is called an automatic leveling apparatus) for automatically performing correction according to change in the running attitude of a vehicle so that the irradiation direction of a lamp (or headlamp) mounted to the vehicle is maintained in a fixed direction.
For example, there is known a conventional apparatus in which a vehicle height sensor is attached to each of front and rear wheels of the vehicle. Alternatively, there is known another conventional apparatus in which a vehicle height sensor is attached only to one of the front and rear wheels thereof. Such an apparatus obtains a change in the pitch angle (or pitching angle) of the vehicle according to detection information acquired by the height sensor, and controls the irradiation direction of the lamp or controls the height of a cut-off line in a low beam light distribution pattern by driving a reflecting mirror provided in the headlamp so as to cancel the change in the pitch angle.
Further, preferably, the control response of an automatic leveling apparatus is changed according to the magnitude of an acceleration of a vehicle. Thus, when the magnitude of the acceleration is large, fast control is performed. Conversely, when the magnitude of the acceleration is small, slow control is performed.
Further, when the irradiation direction of the lamp unnecessarily largely changes during the vehicle drives on a rough road, the visibility may be reduced. In view of control stability, such a conventional apparatus employs a moving average method of setting a definite time (hereunder referred to as a xe2x80x9cdetecting windowxe2x80x9d) correspondingly to vehicle height data collected for every constant period (or sampling period) or to pitch angle data based on the height data and computing an average value of such data in the definite time (incidentally, as time elapses, each of the starting and end points of the detecting window moves by a unit time). The control of the irradiation direction of the lamp is performed according to this moving average value. Thus, attention is paid to the prevention of the irradiation direction control from being too sensitive about change in the vehicle height.
However, in the case that the time width of the detecting window for moving-averaging is not set at a relatively large value in such a conventional apparatus, stable detection data cannot be obtained. Thus, it takes time to calculate a moving average value. For instance, even when significant change in the vehicle height occurs during the moving average value is calculated, such change is neglected by the averaging. This may result in followability deterioration and control delay, and may cause glare.
Accordingly, an object of the present invention is to manage both the stabilization of control of the irradiation direction of a vehicular lamp and the prevention of an occurrence of response delay.
To achieve the foregoing object, according to the present invention, there is provided an irradiation direction control apparatus for a vehicular lamp. This apparatus is adapted to acquire data representing a pitch angle of a vehicle by detecting change in the height of an axle portion corresponding to a pair of front wheels or rear wheels or each of the pairs of front and rear wheels of the vehicle and to change the irradiation direction of a vehicular lamp according to change in the attitude of the vehicle in such a manner as to cancel change in the pitch angle. The apparatus comprises irradiation control means that is operative to calculate a moving average value of data, which represents the change in the height of the axle portion or represents a pitch angle, every constant time period, and to obtain a moving average value of the calculated moving average value, and to control the lamp according to a control signal, which is based on the obtained moving average value, in such a manner as to maintain the irradiation direction in a fixed direction.
Thus, according to the present invention, a moving-averaging process is performed on the average value obtained by a first moving-averaging process performed on data representing change in the height of the axle portion or representing the pitch angle. Thus, the apparatus of the present invention can obtain data, which little varies even in the case of using a detecting window that has a relatively short time width, and can reduce control delay. That is, the present invention eliminates the necessity for enhancing stability by setting the time width of the detecting window at a relatively large value, which is necessary in the case of performing a conventional method. Consequently, the apparatus of the present invention can obtain stable data as an effect of performing a plurality of stages of moving-averaging.